Veteran improv warrior Glen Halls past collaborators have included arranger Gil Evans and Sonic Youth guitarist Lee Renaldo. But trio_muo, a working unit since 2002, is the Ontario-based saxophonist and flutists own chamber ensemble.

As cohesive as it is flexible, the band is filled out by longtime associate, bassist Michael Morse, who shadows the reedists every move like a P.I. on a stake-out; and decades younger percussionist Joe Sorbara. Reveling in ambiguity, most composition titles relate to concepts of geometry, so as to focus the listener on the music itself, with its shifting tonal centres, free time and elastic intervals.

Appearing more formidable than they actually are, the 11 tunes take as touchstones the advances of originals like Ornette Coleman and Thelonious Monk, whose characteristic doubled motif echo in a couple of Hall heads. Recorded with remarkable clarity, most tracks have definite architecture, with Hall sharing space with the other two, even turning to alto flute on Vertex to melodically accompany the others improvisations. Solid and thick-toned, with a touch of sul ponticello interjections, Morse is the CDs rhythmic core, while Sorbara colors the proceedings with cymbal pings, rattling maracas, clapped drum sticks and sonorous drum rolls and bounces.

Although he reveals a plush and luxuriant bass flute tone on Big Ears, a threnody for poet Paul Haines, playing his usual tenor and soprano saxophones Halls expression is assured and unique, moving from peeping, quivering shrills on the smaller horn to undulating, territory-marking sonority on the tenor.